Frances Banahan was born in Ireland, probably in 1855 or 1856, the daughter of Cornelius Banahan, a grazier, and his wife, Margaret McManus. She entered the Brigidine Convent novitiate on 1 February 1873 in Mountrath, County Laois, and was professed as a religious on 24 February 1876, taking the name of Sister Mary Gertrude. In 1882 a letter was received in Mountrath from James Murray, bishop of Maitland, New South Wales, asking for six sisters to teach in the school at Coonamble, a remote settlement in the north-west of the state. Sister Gertrude volunteered and was selected for the new mission.
The sisters left Mountrath on 16 April 1883 and travelled to Australia on the steamship Chimborazo. They were accompanied by four priests for the Australian mission and Father John McKenna from New Zealand. Their journey across country was hazardous, and involved travelling by boat, train, coach, buggy and wagonette. They stopped along the way with the Sisters of Mercy, Dominican Sisters and Sisters of the Good Shepherd. When the nuns arrived in Coonamble on 21 June 1883 they received an enthusiastic welcome.
The first Brigidine school was opened on 9 July 1883 with 50 pupils enrolled. Soon a boarding school was built and Sister Gertrude was appointed bursar. The school flourished and she quickly established herself as a highly competent teacher. She was an astute businesswoman and worked closely with Bishop Murray in the extension of their buildings and the acquisition of property. During summer the sisters had to contend with the scorching sun, mosquitoes, snakes and spiders. Two of the nuns contracted typhoid fever and Sister Gertrude became the principal nurse tending the invalids.
In 1887 she was appointed the first superior of a new foundation in Cooma, to the south. Four more sisters joined her and the school was quickly established. In 1898 the Brigidines were invited to establish a foundation in Masterton, New Zealand, at the request of Father McKenna, who was parish priest there. Sister Gertrude was appointed leader of the new foundation; she was accompanied on her journey by three sisters from Cooma and two from Coonamble.
The nuns arrived in Wellington on 14 December 1898 where they visited the Sisters of Mercy at St Mary's Convent, Wellington. Two days later they travelled by train to Masterton with Father McKenna. There they were warmly welcomed by schoolchildren and parishioners, who provided a meal, a well-stocked pantry and a purse of £30.
Sister Gertrude was superior in Masterton until 1908. She and Sister Mary Teresa Flynn were the first religious teachers in Wairarapa, and they commenced St Bride's Convent school with only 11 pupils. The teaching of music and singing became a lasting tradition. Sister Gertrude was soon renowned for her hospitality, generosity, cheerfulness and courage, but she also displayed considerable business acumen and skills in property development. The convent buildings were extended and in 1903 a novitiate was established. More land was purchased and the boarding school thrived; in 1909 a new brick chapel was opened. However, the community suffered a set-back between 1910 and 1912 when three of the young sisters died.
In 1906 Sister Gertrude opened a new foundation in Pahiatua and sent four sisters there from Masterton. Further foundations were opened in Foxton (1911), Carterton (1917) and Johnsonville, Wellington (1929). Sister Gertrude journeyed to Sydney in 1911 to attend a provincial chapter of the order, returning later that year to a further term as superior in Masterton. Sister Joseph Flahavan, one of the pioneering sisters, was appointed superior in 1918. In 1920 Sister Gertrude travelled to Ireland to attend the general chapter in Tullow, County Carlow. She returned to New Zealand in 1921 and was appointed superior in Pahiatua. There she endeared herself to the whole parish community. In 1926 she celebrated the golden jubilee of her profession. A marble altar erected in St Bride's Convent chapel that year was a fitting tribute to Sister Gertrude's determination to save donations and all money discounted on bills from the beginning of the foundation. They used the money she had saved to purchase the altar.
In 1930 Monsignor McKenna died and his loss was keenly felt in all Brigidine communities. Sister Gertrude's health deteriorated in 1931 and she died in Pahiatua on 17 March 1932. Her remains were brought back to St Bride's chapel in Masterton and she was buried in the Masterton cemetery on 19 March.
Sister Gertrude was a fine religious teacher and a clever businesswoman. Those who came in contact with her recognised the depths of her kindness and compassion, her contribution to education and the arts and her intelligent interest in many subjects. Her qualities of leadership were remarkable, and she inspired and was instrumental in bringing about the expansion of the Brigidine congregation both in New South Wales and in Wairarapa.